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Metal presence in the aquatic ecosystem has increased and diversified over the last decades due to anthropogenic sources. These contaminants cause abiotic stress on living organisms that lead to the production of oxidizing molecules. Phenolic compounds are part of the defense mechanisms countering metal toxicity. In this study, the production of phenolic compounds by Euglena gracilis under three different metal stressors (i.e. cadmium, copper, or cobalt) at sublethal concentration was assessed using an untargeted metabolomic approach by mass spectrometry combined with neuronal network analysis (i.e. Cytoscape). The metal stress had a greater impact on molecular diversity than on the number of phenolic compounds. The prevalence of sulfur- and nitrogen-rich phenolic compounds were found in Cd- and Cu-amended cultures. Together these results confirm the impact of metallic stress on phenolic compounds production, which could be utilized to assess the metal contamination in natural waters. [ABSTRACT FROM AUTHOR]

Industrial development and urbanization has led to the diverse presence of metals in wastewater that are often improperly treated. The microalgae Euglena gracilis can tolerate high concentrations of metal via the excretion of organic metabolites, including phenolics. This study aims to evaluate how carbon amendment stimulates phenolic compound production by E. gracilis. The number, relative intensity and molecular composition of the phenolic compounds were significantly different between each of four carbon amended cultures (i.e., glutamic acid, malic acid, glucose, reduced glutathione) during the log phase. Phenolic compounds were mainly produced during the minimum growth rate, likely a response to stressful conditions. A better understanding of phenolic compounds production by E. gracilis and the impact of growth conditions will help identify conditions that favor certain phenolic compounds for dietary and metal chelation applications. [ABSTRACT FROM AUTHOR]

Environmental contamination is an increasing problem and one of the main threats to human health. While euglenoids have been shown to tolerate high levels of metals, little is known about the metabolic mechanisms at play. To address this gap, Euglena gracilis cells in the mixotrophic exponential phase were exposed to high levels of cadmium (Cd), cobalt (Co), or copper (Cu) (2.7–190.7 mg L−1) and the cellular metabolic profiles were explored using a multi-pronged untargeted approach. The combined application of proton nuclear magnetic resonance (1H NMR) and high-resolution mass spectrometry (HRMS) expanded the coverage of detected metabolites by 38–58 % using the computational platform Pathos and the metabolite databases KEGG, Metlin, and Chenomx. Only 3 % of the identified metabolites were found to be common to 1H NMR and HRMS. This low overlap indicates that the two methods complement each other, with each method uncovering a unique set of metabolites. Although four metabolic pathways including purine metabolism, alanine, aspartate, and glutamate metabolism, and the citrate cycle were common to all metal treatments, sixteen metabolic pathways were metal-specific. Notably, the metabolic alterations induced by Cd and Co differed from each other and the control, while the metabolic profile of Cu-treated cells resembled the control more closely. Unlike Co which showed a broad impact on Euglena gracilis metabolism, the stress induced by Cd and Cu exposure seems to target more the amino sugar production and the chlorophyll machinery, respectively. The observed metabolic alterations in response to various metals highlight a potential correlation with the generation of reactive oxygen species (ROS). Together these results contribute to a better understanding of cellular toxicity and the impacts of metal-induced oxidative stress in Euglena gracillis cells. • Cd, Co, and Cu stress triggered adaptive responses in Euglena gracilis. • Remodeling of amino acid metabolism and adjusting energy metabolism were observed. • The Cu treatment exhibited a milder effect on the metabolic profile. [ABSTRACT FROM AUTHOR]

Euglena gracilis is a single-celled, free-living flagellate that grows in a variety of cultivation conditions. In this study, we investigated the effects of calcium acetate, glucose, glutathione (GSH), glutamic acid, and malic acid additions on the growth and metabolism of heterotrophic E. gracilis cells. To analyze the metabolic changes, size exclusion liquid chromatography-mass spectrometry was employed, enabling the comprehensive examination of the metabolomics changes in response to the carbon sources. The addition of glucose and GSH led to relatively high cell count production, whereas moderate cell count production was observed with the use of calcium acetate, glutamic acid, and malic acid, synonymous with less favorable growth conditions. Common enriched pathways (i.e., cysteine and methionine metabolism, purine metabolism, pentose phosphate pathway (PPP), and glyoxylate and dicarboxylate metabolism) were found in all carbon treatments, highlighting their critical role in the basic Euglena gracilis metabolism. Moreover depending on the carbon source, some metabolites associated with the amino acid, lipid, and vitamin metabolisms were significantly enriched. These findings provided valuable insights into the metabolism of E. gracilis regarding its diverse metabolic responses to carbon source changes. • The change in organic carbon sources favors some metabolites over others. • The malic acid treatment revealed more changes in the amino acid pathways. • The folate pathway was enriched in the glutathione and malic acid treatments. [ABSTRACT FROM AUTHOR]